/ETH-dapp-coding-challenge

The goal of this challenge is to create your own ERC20 Token and a Token Vendor Contract that will handle the sell/buy process of your token exchanging it with ETH sent by the user.

Primary LanguageJavaScriptMIT LicenseMIT

ERC20-buy-sell-exchange

The goal of this challenge is to create your own ERC20 Token and a Token Vendor Contract that will handle the sell/buy process of your token exchanging it with ETH sent by the user.

Setup

  • Init hardhat project:
mkdir hardhat && \
cd hardhat && \
yarn init --yes && \
yarn add -D hardhat

yarn add -D hardhat-deploy hardhat-deploy-ethers ethers chai chai-ethers mocha @types/chai @types/mocha @types/node typescript ts-node dotenv # For hardhat framework
yarn add -D @openzeppelin/contracts # security
  • If modify some things, re-run install yarn install

🚩 Challenge 1: 🥩 Decentralized Staking App

1. Exercise Part 1: Implement the stake() method

  • In this part of the exercise, we want to allow users to stake some ETH in our contract and track their balances.

  • uint and uint256 are the same (it’s just an alias)

  • when a variable is declared public, Solidity will automagically create a getter method for you. This means that it will expose a yourVariableName() method to be called

  • when you declare a variable without initializing it, it will be initialized to its default value based on the variable type Solidity exposes some utility units like wei, ethers, or time units.

  • Working dir: cd hardhat

  • Run node: yarn chain

  • Run test: yarn test

  • Compile contracts: yarn compile

  • Run frontend: yarn start

  • Using hardhat-deploy to deploy the contracts, an Hardhat Plugin to better manage deployment

2. Exercise Part 2: Implement the lock mechanism and withdraw

  • These conditions are:
    • At least 1 ETH needs to be stacked on the Staker Contract
    • The 1 ETH stack threshold is reached within a time deadline of 30 seconds
  • Concepts
    • Modifier
    • Error handling
    • Transfer, send, call ether

🚩 Challenge 2: 🥩 ERC20 and Token Router Contract to buy/sell your own token

Exercise Part 1: Create your own ERC20 Token and deploy it!

  • Concepts:

    • OpenZeppelin ERCO20
    • Ethereum ERC-20 Standard
    • Inheritance
    • Shadowing inherited State variables

  • Inhering OpenZeppelin ERC20

  • Minting owner token

  • Writing unit tests:

    • Checking name, symbol and total supply are exactly.
    • Checking transfer the token from the owner to a user

Exercise Part 2: Create a Router Contract
The Router contract will be responsible to allow users to exchange ETH for our Token
We need to:

  • Set a price for our token (1 ETH = 100 Token) (in deployment time or testing)
  • Implement a payable buyToken() function
  • Transfer all the Tokens to the Router contract (in deployment time or testing)

Concepts:

  • Events
  • Payable functions
  • Openzeppelin Ownable, ownership
  • Openzeppelin address utility
  • Transfer and send token

Exercise Part 3: Allow the Router to buy back!
The flow that will happen:

  • The user requests to “approve” the Router contract to transfer tokens from the user’s balance to Router's wallet (this will happen on the Token’s contract).
  • When you invoke the approve function you will specify the number of tokens that you want to decide to let the other contract be able to transfer at max.
  • The user will invoke a sellTokens function on Router contract that will transfer user’s balance to Router’s balance
  • The router's contract will transfer to the user’s wallet an equal amount of ETH

Concepts:

  • ERC20 function approve
  • ERC20 function transferFrom